Axial flow compressor



Feb. 18, 1964 .LJERIE ETAL 3,121,527

AXIAL FLOW COMPRESSOR Filed Dec. 4, 1962 2 Sheets-Sheet 1 Al .Jh-25 Feb. 18, 1964 J. JERIE ETAL 3,121,527

AXIAL FLOW COMPRESSOR Filed Dec. 4, 1962 2 Sheets-Sheet 2 BY @Za/@n4 United States Patent O 3,121,527 AXlAL FLW CGMPRESSGR .lan Jerie, 27 Eomornielra, and Miroslav Vlaslr, ll Na Krutnici, both of Prague 6, Czechoslovakia Filed Dec. 4, 1962, Ser. No. 242,287 Claims priority, application Czechoslovakia Dec. l5, 1961 2 Claims. (Cl. 23d-m2) The invention relates to 'axial flow compressors, and more particularly to an axial flow compressor of improved efficiency, lower peripheral speed and reduced dimensions for equal compres-sion per stage `and flow rate as compared to conventional compressors.

The term compressor as employed in this speciication and the appended claims will be understood to include blowers, fans, `and like devices having alternating rows or stages of rotary and stationary blades, and means for actuating rotation oi the rotary blades whereby movement cr liow of a iluid substantially parallel to the axis of rotation is generated.

l -xial compressors `are commonly employed in gas turbines, and lind a wide tield of application in the chemical processing and other industries. Axial compressors have generally higher eliiciency, lower weight, and smaller overall dimensions than centrifugal compressors of comparable capacity.

The kinetic energy spent in actuating rotation of the compressor rotor is stored in the flowing gas as it is being compressed. During compression, the gas particles ow along substantially cylindrical surfaces. The flow path of the gas particles along these surfaces is determined by the shape and arrangement of the blades.

It is customary to arrange the blades of an axial compressor in such a manner that the blade reaction is approximately 5G percent. The low coefcient o which expresses the ratio of the yaxial iow veloci-ty wa of the compressed gas to the peripheral veloci-ty u of the blades has an approximate value of 0.5 in such an arrangement. The blades of an axial compressor have also previously been arranged Afor a higher reaction, even exceeding 100 percent, and the eliicie cy of the compressor may be raised to a limited extent by a higher reaction percentage.

The object of this invention is `an improvement in the eiiiciency of the known axial ilow compressors and/or reduction of power input, compressor size and rotor speed as compared to known axial flow compressors of comparable capacity substantially beyond the improvement available by adjustment of the blade reaction.

Other objects and many of the attend-ant advantages of this invention will be readily appreciated as the same be* comes better understood as the disclosure proceeds.

For a better understanding of this invention, the attached drawing illustrates operational characteristics and structural features of known axial flow compressors as well as corresponding characteristic-s and features oi a compressor according to the instant invention.

The several portions of FlG. l relate to a conventional compressor having a blade reaction of percent, FlG. la being a diagram or" velocity relations, FIG. lb being a fragmentary radial view of the blades of the compressor, and FIG. lc being a fragmentary developed diagram of the cylindrical surface in which a gas particle moves.

The several portions of FG. 2 relate to a conventional vcompressor having a blade reaction `of lGG percent. FIGS. 2a, 2b, and 2c respectively illustrate velocity relations, the structural arrangement of the blades, and the llow path of a gas par-ticle in such a compressor in a manner analogous to FIGS. la, lb, and 1c.

FIG. 3 relates to a compressor of the invention, and the constituent parts of FIG. 3, namely, FIGS. 3a, 3b, 3c, correspond to the parts of FlGS. l and 2 identified by the same suffixes.

l'lil Patented Feb. i8, i964 p ICC Referring initially to FIG. la lthere is seen the vector diagram correlating the peripheral speed u of the rotor blades in a compressor stage with the velocities of the gas particles. The vectors w1 and W2 represent the velocities of the gas relative to the rotor resulting from the vectorial combination of the absolute air stream velocities w3 and W4 with the roto-r velocity u. The deviation of `the velocities w1 to W4 from an axial velocity wa are indicated by angles al to a, respectively.

FlG. 1b shows two rotor blades R and Itwo stator blades S in 'two laxially successive rows of compressor blades separated by a clearance space m inthe axial direction indicated by the arrow A. The `blades are airfoils as is customary. The rotor blades R move relative to the stator lades S in the direction of :the arrow u during operation of the compressor. It will be appreciated that FIG. lb merely shows a small fragment of a conventional compressor in which the blades S are mounted lixedly in a housing of substantially circular cross section, and the blades Rare mounted on a corresponding rotor body connected by a shaft to a source of driving power for rotation in the housing. The number of alternating rows of rotor and stator blades may be selected at will as is well known, and each circular row of blades includes a plurality of blades circumferentially spaced from each other in the manner evident from FIG. =lb.

The path of a gas particle in a substantially cylindrical surface about the .compressor axis is illustrated in FIG. lc in la developed View of lthe surface which intersects stator blade rows S0, S1 and rotor blade rows R1 Iand R2. The blades S0 constitute the intake stator blades of a cascade, the blades R1 and S1 jointly constitute the first compressor stage, and the blades R2 together with sta-tor blades S2 not shown in FIG. lc constitute a second compresso-r stage. 'llie path of a gas particle relative to :the moving rotor is indicated by the lbroken line dm, and its path relative to the stationary elements of the compressor by the fully drawn line 134. The lines du and 34 diverge in ythe axial cw direction.

Under the conditions of 50 percent blade reaction illustrated in FlG. l, the path dm of each gas particle deviates substantially from the direction or the rotor axis. The inclination of the several portions of the path varies between limits dened by the angles a3 and a4 in FlG. la. Relative to the stationary compressor parts, the gas particles tlow in a generally helical path about the compressor axis. The path deviates laterally from a true helix by undulations where the gas particles are deflected by the rotor and stator blades. The path du of each individual gas particle relative to the moving rotor also coustitutes a helix but of opposite lead angle varying between extreme values represented by the angles el and e2 in HG. la. 'In the compressor having a blade reaction of 50 percent to which FIG. l relates, the lead angles or inclinations of paths 112 and e234 are opposite and equal in magnitude on the substantially cylindrical surface considered.

FIG. 2 illustrates features and characteristics of an axial ilow compressor ditlering from the compressor of FIG. l only by its blades R and S which are arranged for l0() percent reaction. The helical path of each gas particle relative to the stator of the compressor is represented in FIG. 2c by the solid line 134 which may be termed a helix having a lead angle of with such deviations as are inherent in the interaction between the gas particles and the blades S0', R1', S1', R2', etc. The inclination of the line d34 relative to a line parallel to the rotor axis may vary between the angles a3 and er' in FlG. 2a which are respectively delined by the vectors w3', W4 and wa in a manner evident from the preceding description of HG. l. The path dlg of the gas particles relative to the rotor of the compressors to which FIG. 2

relates is inclined relative to an axial line by an angle which -varies between the va'lues al and a2 deiined in FIG. 2a by the vectors w1', W2 and wa. The path of each gas particle relative to the rotor is thus much longer than in the compressor of FIG. 1 and the path relative to the stator is shorter. The smaller the lead angle, the longer the flow path, and the greater the energy losses.

lt is evident from the preceding discussion of FIGS. l and 2, that an attempt at lowering energy losses in a compressor by shortening the path of the ilowing fluid relative to the stator necessarily causes a lengthing of the path relative to the rotor. Only an insigniiicant gain in efficiency is thus available by adjustment of the blade reaction.

We have Ifound that it is possible to modiiy the basically known structure of an axial ilow compressor in such a manner that the lengths of the flow paths relative to the stator and to the rotor are simultaneously shortened. The relevant features and characteristics of a compressor of the invention are illustrated in FiG. 3 in which elements designated by double primed reference characters correspond to elements indicated by unprimed reference charactersy in FIG. 1 and by primed reference characters in FiG. 2.

One factor important for simultaneously shortening the ilow paths of the gas particles in the compressor of our invention resides in control of the direction of gas llow in each space m between axially successive rows of rotor and stator blades. lt will be assumed for the purpose of the disclosure that these spaces are uniform between the several rows, but the assumption is not relevant to this invention. The direction of llow in each space m must not be inclined more than 45 with respect to a corresponding axial plane.

In `an otherwise conventional compressor, such an arrangement would result in excessive shortening of the blade length. S-hortening of the path along the blades would be achieved in such a manner, and the friction losses due to relative movement of the flowing medium and the blade surfaces would be decreased Losses due to secondary effects of the blade shortening, however, would practically balance any gain in eh'iciency which might be achieved by merely controlling the flow path in the space m. Two additional conditions must be simultaneously met.

A second necessary condition for improved efficiency in the axial ilow compressor of our invention is proper relationshipV between the compressor dimensions which permits the compressor to be operated in such a manner that the conditions of the following Equation l are met:

ln this equation, D 1s the effective rotor diameter in meters as measured between the radially outermost tips of diametrically opposite rotor blades, n is the rotor speed in revolutions per minute, and V is the `tlow volume in cubic meters per second. The product of the cube of the effective compressor diameter in meters and of the rotary speed in reciprocal minutes should not be more than fty times greater than the ilow volume in cubic rneters per second.

When the conditions of( the above equation are met, the blades have a reasonable length, and the secondary .losses yare held to reasonably low values. Fully to achieve the objects or" Vthis invention, we have found it necessary to meet a third condition. The stator blades and the rotor blades must be airfoils having a maximum thickness of not more than twelve percent oi the length of the chord.

' When the above three conditions are met, it is possible to substantially reduce the overall dimensions or" an axial `ilow compressor as compared to the dimensions of a conventional compressor of equal capacity.V The cciency of the `apparatus is increased. The peripheral speed of the rotor blades necessary for a predetermined compression ratio in a stage is lower in our compressor than in a conventional compressor of equal compression ratio. The energy input for a given compression etect is lower with a corresponding decrease in operating cost. The smaller compressor of our invention is inherently lower in -iirst cost than a compressor of customary design, and occupies less space. lt is driven by a smaller, and less bulky motor under otherwise comparable conditions.

Certain important features of our invention will be best understood oy reference to the several portions of FIG. 3. FiG. 3a shows the vector diagram correlating the peripheral speed n of the rotor blades R in a compressor stage with the velocities of. `the gas particles in a manner analogous to FiG. la. FiG. 3b shows rotor blades R and stator blades S of axially successive rows separated by a space m, FIG. 3c is a developed view of the Y cylindrical plane in which a particle travels through two compressor stages respectively represented by cooperating rotor and stator blades R1, S1 and R2, S2. The paths oi the particles relative to the rotor and to the stator are respectively indicated by lines dlg and (1134,.

FIG. 3b also shows the angle [i2 defined by a tangent drawn on the mean line of the airfoil constituting a rotor lade at the trailing edge thereof, and by a line parallel to the axis drawn through the point of intersection of the tangent with the trailing edge. This angle [52 will hereinafter be referred to as the outlet angle of the airfoil We have found that the outlet ansie of each airtoil` constituting a rotor blade should not exceed 40, and does not exceed 40 ir the etere-mentioned three conditions are met.

The iiow paths of the gas particles relative to the rotor and stator of our compressor are very short as compared to otherwise similar conventional axial flow compressors. The losses resulting from irictional contact between the gas particles and the airfoil surfaces are correspondingly reduced. it is evident from FIG. 3o that the peripheral rotor velocity u necessary to produce a given rate wa of axial low is low. High flow rates can thus be achieved with a compressor of relatively small eiiective rotor diameter, at relatively loul rotary speed. Since the ilow coefficient cp is high, the energy transmitted to the flowing iiuid by the rotor is great even at relatively low peripheral rotor speed, and the com: pression ratio obtained in each stage is high, and higher than available in otherwise comparable compressors of usual design.' Y

The vector diagram of FIG. 3o, of course, is merely typical of a compressor of this invention, and modifications of the comp essor represented by modified diagrams will readily suggest themselves to those skilled in the art. The compression ratio in each stage may be altered and thershape oi the characteristic lines (112 and 34 may be correspondingly changed by varying the percentage reaction of the blades.

Whatever secondary changes may be introduced, it is essential that the three principal features of the invention enumerated above be adhered to, namely:

(l) The'direction of ilow in the space axially interposed between successive rows of stator and rotor blades should not be inclined by an angie of more than 45 to the direction of the rotor axis;

(2) rl'he conditions or Equation i must be met; and

(3) The airioils constituting the rotor blades must not have a thickness greater than l2 percent of the chord length.

Within these limitations, many modifications and variations of the present invention are possible in the light of the above teachings. it is therefore to be understood that within the scope of the appended claims, the invention ay be practiced otherwise than as speciiicaliy described.V

What we claim is: means about said axis at a S13-eed sufficient to canse 1. An axial ow compressor comprising, in combinaflow of said gas in said stream at a predetermined tion: rate, the product of the cube ot said eeotive diam- (a) stator means having an axis; eter in meters times said speed in revolutions per (15) rotor means rotatable about said axis; 5 minute not being greater than fty times said rate (C) said stator means and rotor means each including in cubic meters per second.

a plurality of airoil blades arranged in axially alter- 2. A compressor as set forth in claim 1, wherein each nating rows on said stator means and on said rotor airfoii blade has a profile mean line and a trailing edge, means for guiding a stream of gas in an axially eX said mean line intersecting said trailing edge in a point, tending path, the spacing of the radially outermost 10 a tangent drawn on said mean line at said point and a portions of diametrically opposite blades on said line drawn parallel to said axis through said point derotor means dening the eective diameter of said ning an output angle not greater than 4G degrees.

rotor means;

(d) each row of said airtoil blades on said rotor References cmu mthe me of this patent means defining with two axially adjacent rows of 15 UNITED STATES PATENTS said airfoil blades on said stator means respective 2,373,372 Whittle june 12, 1945 spaces therebetween, said path having respective por- 2,505,755 Gamm @t 1 May 2, 195() tions in said spaces, each of said portions being in- 2,605,956 Gargnef Aug, 5, 1952 clined relative to said axis at an angle not greater 2,563,493 146551 Dec, 22, 1953 than 45 degrees; 20

(e) the thickness of each of said airfoil blades being FGRDGN PATENTS not greater than twelve percent of the chord length 528,950 Canada June 25, 1949 thereof; and 632,960 Canada Oct. 12, 1956 (f) actuating means for actuating rotation of said. rotor 855,891 Germany Nov. 17, 1952 

1. AN AXIAL FLOW COMPRESSOR COMPRISING, IN COMBINATION: (A) STATOR MEANS HAVING AN AXIS; (B) ROTOR MEANS ROTATABLE ABOUT SAID AXIS; (C) SAID STATOR MEANS AND ROTOR MEANS EACH INCLUDING A PLURALITY OF AIRFOIL BLADES ARRANGED IN AXIALLY ALTERNATING ROWS ON SAID STATOR MEANS AND ON SAID ROTOR MEANS FOR GUIDING A STREAM OF GAS IN AN AXIALLY EXTENDING PATH, THE SPACING OF THE RADIALLY OUTERMOST PORTIONS OF DIAMETRICALLY OPPOSITE BLADES ON SAID ROTOR MEANS DEFINING THE EFFECTIVE DIAMETER OF SAID ROTOR MEANS; (D) EACH ROW OF SAID AIRFOIL BLADES ON SAID ROTOR MEANS DEFINING WITH TWO AXIALLY ADJACENT ROWS OF SAID AIRFOIL BLADES ON SAID STATOR MEANS RESPECTIVE SPACES THEREBETWEEN, SAID PATH HAVING RESPECTIVE PORTIONS IN SAID SPACES, EACH OF SAID PORTIONS BEING INCLINED RELATIVE TO SAID AXIS AT AN ANGLE NOT GREATER THAN 45 DEGREES; (E) THE THICKNESS OF EACH OF SAID AIRFOIL BLADES BEING NOT GREATER THAN TWELVE PERCENT OF THE CHORD LENGTH THEREOF; AND (F) ACTUATING MEANS FOR ACTUATING ROTATION OF SAID ROTOR MEANS ABOUT SAID AXIS AT A SPEED SUFFICIENT TO CAUSE FLOW OF SAID GAS IN SAID STREAM AT A PREDETERMINED RATE, THE PRODUCT OF THE CUBE OF SAID EFFECTIVE DIAMETER IN METERS TIMES SAID SPEED IN REVOLUTIONS PER MINUTE NOT BEING GREATER THAN FIFTY TIMES SAID RATE IN CUBIC METERS PER SECOND. 